Parental Care Patterns How much care to provide? Who should provide care? When should care be terminated? Who should receive care?

Insect parental care

Distribution of parental care in vertebrates Teleost fishes = 21% of families show PC 61% have male parental care Amphibians = 71% show PC 50:50 maternal:paternal Birds = 100% show PC Usually biparental, sometimes one sex Mammals = 100% show PC Usually maternal, sometimes biparental

How much care to provide? Parental investment: “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving at the cost of the parent’s ability to invest in other offspring (Trivers 1972) Costs of parental care include Reduced future survival Reduced mating opportunities

Parental investment changes

Parental care decreases survival in willow tits

Parental care decreases mating opportunities A female-biased sex ratio increases the cost of brood care for males because parental care detracts from mating

Alternative hypotheses for providing care Confidence of paternity Expect parent with highest certainty to be parental Order of gamete release First to deposit gametes can desert Association Sex nearest to offspring when care is needed

Parental care in fishes and frogs

Alternative hypotheses for providing care: evidence Confidence of paternity (fish and herps) Internal fertilization - 86% maternal care External fertilization - 70% paternal care Order of gamete release Simultaneous fertilization (most species) - 78% paternal Other species - male deposits first, but doesn’t leave Association Territorial males have external fertilization

Why male parental care? Randall’s jawfish Mallee fowl

Growth, fecundity and paternal care

Parental care can cost females more than males Mouthbrooding results in weight loss due to reduction in feeding, and the cost of brood care is higher in females than males

Parent-offspring conflict

Parent-offspring conflict Wallaby conflict Assume fixed total resource that can be used to feed offspring Parents want to distribute resource equitably to all n offspring Offspring want more than 1/n but not all since they are related to siblings Difference between parent and offspring optimum increases as relatedness decreases

Parent-offspring conflict: how much care to provide Parent is equally related to all offspring, but offspring are less related to sibs than themselves. Assuming full siblings, i.e. r = 1/2 B - measured in +units of RS of current offspring C - measured in - units of RS of future offspring B C/2 Max. inclusive fitness for offspring C Benefit or cost to parent Max. inclusive fitness for parent Level of parental investment

Begging loudness increases as relatedness within nest decreases Brown-headed cowbird

Parent-offspring conflict: time of weaning (Full-sibs) (Half-sibs)

Parental investment and maternal age If reproductive value declines with maternal age, then older females should be willing to expend more on parental care

Who should receive care? Concorde fallacy: past investment should not determine future investment - only prospects for future success Expect parents to use honest indicators of offspring quality to allocate care

Sibling competition

Sibling conflict

Chick color affects parental feeding in mixed broods of coots Control broods were unaltered (orange) or had orange feathers trimmed (black) Experimental broods had 1/2 orange, 1/2 black chicks Chick color likely indicates offspring health